a,b,or e? heads--- weird possibly dumb question

lookin up headers for my 360 73 duster and.....:banghead:

hedman headers say a type engine only http://www.jegs.com/i/Hedman/500/78050/10002/-1

hookers say b-a heads, but stock are different??
http://www.jegs.com/i/Hooker-Headers/520/5901/10002/-1

and finally jegs headers say nothing.
http://www.jegs.com/i/JEGS-Performance-Products/555/30080/10002/-1

i guess i am more curious on what hooker is trying to say by a-b engine and that it will need modifying?? maybe im thinking too much, or its too late.

either that or i am asking a really ridiculous question, because my motor is an la motor. is that what they are referring to?:newb: